Implement custom element construction and some 'define' checks

third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp

Index: third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
diff --git a/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp b/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
index acb4cfcd292594344964e315ca59425eaed2fd62..ca410ef58a8a9013af839fbca1ad794c770e9219 100644
--- a/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
+++ b/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
@@ -1324,8 +1324,10 @@ void LocalDOMWindow::cancelIdleCallback(int id)
 
 CustomElementsRegistry* LocalDOMWindow::customElements() const
 {
-    if (!m_customElements)
-        m_customElements = CustomElementsRegistry::create();
+    if (!m_customElements && frame()) {
+        ScriptState* scriptState = ScriptState::forMainWorld(frame());

[haraken, 2016/05/10 09:04:22]

Can you add [CallWith=ScriptState] to Window.customElements and pass in the
ScriptState from the binding layer?

[dominicc (has gone to gerrit), 2016/05/11 02:31:49]

We actually really need to construct that object in the main world; I put some
details in a reply to CustomElementsRegistry. It's about the map that object
maintains needs to be in the main world isolate.

[haraken, 2016/05/11 06:25:28]

It's nasty to manipulate V8 objects in a different world... (It has a risk of
leaking wrappers between worlds.)

Would it be an option to simply disallow the isolated world to access
customElements until you implement per-world CustomElementsRegistry correctly?

+        m_customElements = CustomElementsRegistry::create(scriptState);
+    }
     return m_customElements.get();
 }